Abrasion - Physical wearing and grinding of
a surface through friction and impact by material carried
in air, water, or ice.

Absolute
Humidity - Measurement of atmospherichumidity.
Absolute humidity is the mass of
water vapor in a given volume o
air (this measurement is not influenced by the
mass of the air). Normally expressed in grams of
water vapor per cubic meter of atmosphere at a
specific temperature.

Absorption (Atmospheric) - Atmospheric absorption
is defined as a process in which solar
radiation is retained by a substance and
converted into heat
energy. The creation of heat energy also
causes the substance to emit its own radiation.
In general, the absorption of solar radiation by
substances in the Earth's atmosphere results
in temperatures that get no higher than 1800° Celsius.
According to Wien's
Law, bodies with temperatures at this level
or lower would emit their radiation in the longwave
band.

Abstract
Space - Geographic model or representation
of the real world. For example, maps and globes
are abstractions of the real world or concrete
space.

Abyssal
Fan - Fan shaped accumulation of sediment
from rivers that is deposited at the base of a submarine
canyon within an ocean
basin.

Accumulation
Zone - (1) Region in a glacier where
there is a surface net addition of snow. (2) Part of a hillslope that has
a net gain of material leading to a progressive
raising of the slope's surface.

Adaptation - (1) Evolutionary adaptation - a
genetically based characteristic expressed by a
living organism. Particular adaptations found in populations become
frequent and dominant if they enhance an individual's
ability to survive in the environment. (2) Physiological adaptation -
change in an organism's physiology as a result
of exposure to some environmental condition.

Adaptive
Radiation - The evolution of
a number of new species from
one or a few ancestor species over many thousands
or millions of years. Normally occurs after a mass
extinction creates a number of vacant ecological
niches or when a radical change in the
environment produces new ecological niches.

Adiabatic - A process in which heat does
not enter or leave a system. In the atmospheric
sciences, adiabatic processes are often used to
model internal energy changes in rising and descending
parcels of air in the atmosphere.
When a parcel of air rises it expands because of
a reduction in pressure.
If no other non-adiabatic processes occur (like
condensation, evaporation and radiation), expansion
causes the parcel of air to cool at a set rate
of 0.98° Celsius per 100 meters. The opposite
occurs when a parcel of air descends in the atmosphere.
The air in a descending parcel becomes compressed.
Compression causes the temperature within the parcel
to increase at a rate of 0.98° Celsius per
100 meters.

Adiabatic
Cooling - The cooling of a rising parcel
of air due to adiabatic processes.

Advection - Process that involves the transfer
of mass and heat energy by
means of horizontal motions through a fluid substance like air or water.
Also see convection.

Advection
Fog - Fog generated
when winds flow over a surface with a different
temperature. Two types of advection fog exist.
When warm air flows over a cold surface it can
produce fog through contact cooling. Cold air blowing
over a warm moist surface produces a form of advection
fog know as evaporation
fog.

Agronomy - Field of science that studies phenomena
related to agriculture.

AHorizon - Soilhorizon normally
found below the O
horizon and above the B
horizon. This layer is characterized by
the following two features: (1) A layer in which humus and
other organic materials are mixed with mineral
particles. (2) A zone of translocation from
which eluviation has
removed finer particles and soluble substances.

Air Mass - A body of air whose temperature and humidity characteristics
remain relatively constant over a horizontal distance
of hundreds to thousands of kilometers. Air masses
develop their climatic characteristics by remaining
stationary over a source
region for a number of days. Air masses
are classified according to their temperature and
humidity characteristics.

Air
Pollution - Toxification of the atmosphere
through the addition of one or more harmful substances
in the air. Substance must be in concentrations
high enough to be hazardous to humans, other animals,
vegetation, or materials. Also see primary
pollutant and secondary
pollutant.

AlternativeHypothesis (H1) - Is a hypothesis that
has been suggested because it is believed to be false or because it is to be used as a starting point for scientific argument. Used in statistical testing to organize arguments.

Altocumulus
Clouds - Middle altitude cloud that
is colored from white to gray. This cloud is composed
of a mixture of water droplets and ice crystals.
It appears in the atmosphere as layers or patches
that are well rounded and commonly wavelike. Found
in an altitude range from 2,000 to 8,000 meters.

Altostratus
Clouds - Gray-looking middle altitude cloud that
is composed of water droplets and ice crystals.
Appears in the atmosphere as dense sheet like layer.
Can be recognized from stratus
clouds by the fact that you can see the
Sun through it. Found in an altitude range from
2,000 to 8,000 meters.

Ammonia - Chemical compound composed of nitrogen
and hydrogen (NH3). Component of the nitrogen
cycle. Immediately released from organic
matter upon decomposition.

Ammonium - Chemical compound composed of nitrogen
and hydrogen (NH4). Component of the nitrogen
cycle. Product of organic matter decomposition.
Can be fixed to clay minerals and later exchanged.

Amphibian - Group of vertebrateanimals that
can inhabit both terrestrial and aquatic habitats.
This group of animals consists of frogs, newts,
and salamanders. These organisms live at the land/water
interface and spend most of their life in water.
Descended from fish and ancestors to reptiles.

Amphibole - A group of double chained inosilicateminerals whose
basic chemical unit is the tetrahedron (SiO
4
). They are common rock forming minerals and are found in most igneous and metamorphic rocks.
They form at low temperatures with the presence of water in the crystallization
environment. There are about 60 recognized mineral types in this group.

Anaerobic - (1) Absence of molecular oxygen. (2) Occurring only in the absence
of molecular oxygen. (3) Growing in the absence of molecular
oxygen.

Anemometer - Mechanical instrument used to measure wind speed.
These instruments commonly employee three methods
to measure this phenomenon: 1) A device with three
or four open cups attached to a rotating spinal.
The speed of rotation is then converted into a
measurement of wind speed; 2) A pressure plate
that measures the force exerted by the moving wind
at right angles; 3) An instrument consisting of
a heated-wire where electrical resistance (temperature
of the wire) is adjusted to account for heat lost
by air flow. The faster the wind the greater the
heat loss and thus the more energy that is required
to keep the wire at a constant temperature. As
a result, wind speed is measured through the drain
of electrical current.

Aneroid
Barometer - Barometer that
measures atmosphericpressure via
the expansion and contraction of a sealed hollow
cell which is partially depleted of air.

Angiosperms - Group of vascular plants who
encase their seeds in a mature ovary or fruit.

Angle
of Incidence - Angle at which the Sun's rays or insolation strike
the Earth's surface. If the Sun is positioned directly
over head or 90° from the horizon, the incoming
insolation strikes the surface of the Earth at
right angles and is most intense.

Angle
of Repose - Measurement commonly used in civil
engineering. It is the maximum angle at which a
material can be inclined without failing. Geomorpologist
use this measurement for determining the stability
of slope to mass
movements.

Anticyclone - An atmospheric pressure
system consisting of an area of high
pressure and outward circular surface wind
flow. In the Northern Hemisphere winds from an
anticyclone blow clockwise, while Southern Hemisphere
systems blow counterclockwise.

Aphelion - The point in the Earth's
orbit when it is farthest from the Sun. This distance is bout 152.1
million kilometers (94.5 million miles). Aphelion occurs on the 3rd
or 4th of July. Compare with perihelion.

Applied
Physical Geography - The field of Applied Physical Geography
uses theoretical information from the various fields
of Physical Geography to
manage and solve problems related to natural phenomena
found in the real world.

Aquifer
Recharge Area - Surface area that provides water
for an aquifer.

Archaea - Is a group of recently discovered
organisms that resemble bacteria.
However, these organisms are biochemically and
genetically very different from bacteria. Some
species of the domain Archaea live in the
most extreme environments found on the Earth.

Archaebacteria - Term used to describe organisms
that belong to the biological domainArchaea.

Archean - Geologic eon that
occurred from 2500 to 3800 million years ago. During
this time period, the first single-celled prokaryote organisms evolved and developed.

Archipelago - A group of islands that have an
arc shaped distribution. These islands are usually
of volcanic origin
and are associated with subduction
zones.

Area
Studies Tradition - Academic tradition in modern Geography that
investigates an area on the Earth from a geographic
perspective at either the local, regional, or global
scale.

Arête - Sharp topographic ridge that separates cirques on
a mountain that is or has been glaciated.

Arkose - A type of sedimentarysandstone that
contains a large quantity of weathered feldspar grains.
This type of sedimentary rock forms in arid conditions.

Artesian
Water - Groundwater that
is confined by two impermeable layers beneath the
Earth's surface.

Artesian
Well - A well where the water rises and
flows out to the surface because of hydrostatic
pressure.

Arctic
Circle - Latitude of
66.5° North. The southern limit of the area
of the Earth that experiences 24 hours of darkness
or 24 hours of day at least one day during the
year.

Asexual
Reproduction - Any process of reproduction that
does not involve the fusion of gametes.

Assimilation - (1) Absorption and creation of
food resources. (2) Organic metabolic products
of food digestion. Usually the various organic
constituents of the organism.

Asthenosphere - Zone in the Earth's mantle that
exhibits plastic properties. Located below the lithosphere at
between 100 and 200 kilometers.

Astronomy - Field of knowledge that studies
the nature, motion, origin, and constitution of
celestial bodies.

Atmosphere - The atmosphere is the vast gaseous
envelope of air that surrounds the Earth. Its boundaries
are not easily defined. The atmosphere contains
a complex system of gases and suspended particles
that behave in many ways like fluids. Many of its
constituents are derived from the Earth by way
of chemical and biochemical reactions.

Atmospheric
Pressure - Weight of the atmosphere on
a surface. At sea-level,
the average atmospheric pressure is 1013.25 millibars.
Pressure is measured by a device called a barometer.

Atmospheric
Stability - Relative stability of parcels of
air relative to the atmosphere that surrounds them. Three conditions
are generally described: stable, unstable,
and neutral.

Atoll - A ring shaped reef composed
largely of coral.
These features are quite common in the tropical
waters of the Pacific Ocean.

Atom - Smallest unit of an element that
still maintains its chemical characteristics.

Atomic
Energy - Energy released
from an atomic nucleus because of a change in
its subatomic mass.

Aurora - Multicolored lights that appear
in the upper atmosphere (ionosphere)
over the polar regions and visible from locations
in the middle and high latitudes. Caused by the
interaction of solar
wind with oxygen and nitrogen gas in the
atmosphere. Aurora in the Northern Hemisphere are
called aurora borelisand aurora
australis in the Southern Hemisphere.

Autumnal
Equinox - One of two days during the year
when the declination of
the Sun is at the equator. The autumnal equinox
denotes the first day of the fall season. For the
Northern Hemisphere, the date of autumnal equinox
on either September 22 or 23 (changes yearly).
March 20 or 21 is the date of the autumnal equinox
in the Southern Hemisphere. During the autumnal
equinox, all locations on the Earth (except the
poles) experience equal (12 hour) day and night.

Available
Water - Portion of the capillary
water that is available for plant root
uptake.

Azimuth - A system that measures direction
clockwise from North over 360°.

Azimuthal Projection - Is a two-dimensional map projection where distances and directions are properly depicted from the center point found on a map. This projection has distortion in terms of the shape and size of objects found on this type of map.

Azimuth System - System for determining direction that uses azimuth measurements.